The present invention relates to an apparatus for controlling an operating parameter of an installation, which parameter is related to an electric current feeding a regulation unit operating in switching mode.
A regulation apparatus is known which incorporates an electric modulator designed to operate in conductance control mode. In this type of regulation apparatus the minimum and maximum limits of the current are monitored by a command voltage with a free-running frequency. Such an apparatus conciliates the advantage of a direct limitation of the power module current to the advantage of having a first order transfer function as against a second order transfer function for the conventional regulators. In the conductance control mode regulation apparatus the operation results in a 90.degree. maximum phase shift which compares favorably to the 180.degree. inherent maximum phase shift in the conventional regulators. The conductance control mode regulation apparatus thereby exhibits a substantial progress in the switching regulation art. However this known apparatus is difficult to synchronize. Now the synchronization problem can be of importance in a number of applications. An improvement in the art has already been designed to synchronize a conductance control mode regulation apparatus. This improvement comprises an electric modulator operating with a sole threshold for the current switching, said threshold varying in relation with the sensed current. The modulator uses a synchronization signal for starting the regulation mechanism and the latter ends when the sensed current reaches the switching threshold. This results in a fixed-frequency operation and in the current being controlled to a value which depends on the command signal and the synchronization frequency. Though a fixed-frequency operation is advantageous in that it allows paralleling of several de-phased regulation modules, thereby reducing the filtering mass, this improved apparatus has tendency of instability at certain duty cycles of operation but perhaps the most significant is that the synchronization signal is essential for all paralleled modules to operate, thus requiring a high redundant and complex multiphase synchronization signal generator where reliable and single point failure-free operation is required, e.g. in satellite power regulator applications.
The problem which the invention aims to solve is to provide a regulation apparatus capable of free running operation with current switching mode between two controllable limits as well as fixed-frequency synchronization operation.